The influence of dispersion on the sensitivity of highly birefringent fibers to temperature and hydrostatic pressure was experimentally investigated. In fibers with geometric birefringence that shows high dispersion, great differences were observed between group and phase sensitivities to temperature and hydrostatic pressure. This difference may reach 400% in the case of temperature response. In contrast, in weakly dispersive fibers with stress-induced birefringence these differences were of the order of 8% and 14%, respectively, for temperature and pressure. The influence of the dispersion effect on the temperature compensation of white-light interferometric sensors based on highly birefringent fibers was also discussed.